According to a foil technology, such as is e.g. described in the international patent application with the publication number WO 93/26143 of the same applicants, thin circuit boards are produced from foils or films of an electrically insulating material (e.g. polyimide or epoxy resin) coated on one or both sides with e.g. copper. The production of these foil circuit boards essentially comprises producing conductors and plated through holes on a foil coated on both sides using known photographic and chemical/physical methods. A circuit board obtained in this way with an insulating foil layer and two conductor layers can be laminated together on one or both sides with a further insulating foil (coated on one side with metal) with the aid of in each case an adhesive coating. The further insulating foil or foils are then once again provided with conductors and plated through holes. These method steps can be repeated any number of times, so that foil circuit boards are obtained comprising a plurality of insulating foil layers and a plurality of conductor layers.
As such foil circuit boards are very thin and particularly if they only comprise a few insulating foil layers are also flexible, prior to assembly they are normally laminated onto a rigid substrate, which leads to circuit boards which correspond as regards thickness and format to the normal standards.
If foil circuit boards are built up from several insulating foil layers., their flexibility very significantly decreases, so that in this way, ever without a substrate, very thin circuit boards can be produced which have an adequate natural rigidity, as compared with standard circuit boards, for assembly purposes. Such circuit boards are e.g. used for multichip modules.
As not only the electronic components and the circuit boards assembled therewith are becoming increasingly smaller, but also the equipment and apparatus in which such circuit boards are installed, it would be advantageous in many cases if the circuit boards could be housed in the equipment in such a way as to save more space, i.e. if they could be adapted in an optimum manner, particularly in a flexible or bendable manner with respect to the equipment shape or at least the shape of the equipment inner space allocated thereto. However, it is still necessary for the assembly of circuit boards, to prevent, by adequate rigidity of the circuit board, stresses in the connections between the electronic components and conductors on the circuit board which can be caused by circuit board deformations.